I had a similar experience when I got my '90 MM 4x4 with the V6. I talked to an experienced Mitsu mechanic and he suggested I replace the oil pressure sensor before doing anything else. I think it was around $20 and it turned out the sensor was the problem. That was about 70,000 miles ago and I just started having the same thing happening again, oil light coming on at idle after the engine heats up , especially if I have been pulling a trailer. I intend to replace the sensor again before looking for other causes. I'll let you know if it was the problem.